Cause:GI fluid and electrolyte loss rx'd with Mg-free fluids; malnutrition; fistulae; burns; diuretics; cisplatinum-induced renal disease (Ann IM 1981;95:628)

Pathophys:Low Mg inhibits PTH secretion, which in turn causes hypocalcemic si and sx (Nejm 1970;282:61). Alcohol inhibits PTH secretion, thus also contributing (Nejm 1991;324:721)

Associated with large gi fluid losses and malnutrition, eg, w ulcerative colitis, regional enteritis, chronic alcoholics, toxemia of pregnancy, primary hypo- or hyperparathyroidism, primary hyperaldosteronism, thyrotoxicosis, RTA, diuretic phase of ATN

Sx:Cramps

Si:Carpopedal spasm, Chvostek's si, Trousseau's si, delirium, muscle tremor and bizarre movements, convulsions, hypotension

Ataxias take months to clear

Hypocalcemia; hypo K⁺ in cisplatin type (Ann IM 1981;95:328)

Lab:

Chem:Mg⁺⁺ <1.6 mEq/L. Alkaline phosphatase low

Noninv:EKG shows low-voltage and T-wave abnormalities